This application is a division of U.S. patent application Ser. No. 11/679,513, filed on Feb. 27, 2007, now U.S. Pat. No. 7,704,302.
This invention relates to electrostatic precipitators and, particularly, to limiting sparking in electrostatic precipitators.
Electrostatic precipitators use electrical fields to remove particulates from gas streams, such as, boiler flue gas. Precipitators electrically charge particulates to be removed from gases, and tend not to otherwise affect the gases. Electrostatic precipitators typically have low pressure drops, energy requirements and operating costs.
In an electrostatic precipitator for a boiler, an intense electric field is maintained between high-voltage discharge electrodes, typically wires, bars or rigid frames, and grounded collecting electrodes, typically parallel plates arranged vertically. A corona discharge from the discharge electrodes ionizes the flue gas passing between the collecting electrodes. The ionized gas ionizes fly ash and other particles in the flue gas. The electric field between the discharge electrodes and collecting electrodes drives the negatively charged particles to the collecting electrodes. Periodically, the collecting electrodes are rapped mechanically to dislodge the collected particles, which fall into hoppers for removal.
Sparking can occur between the discharge and collecting electrodes. Sparking limits the electrical energization of the electrostatic precipitator. Sparking occurs when the ionized gas in the precipitator has a localized breakdown such that current rises rapidly and voltage drops between one or more electrodes.
Sparking in an electrostatic precipitator can reach tens of thousands of Amperes, while normal operating currents rarely exceed 2 Amps in a precipitator. Sparks between electrodes create a current path that disrupts an otherwise even distribution of current in the electric field between electrodes. Sparking can damage internal the electrodes and other components of an electrostatic precipitator. The fast transients in current and voltage caused by sparking can also damage and fatigue the precipitator and electrical components in and connected to the precipitator. There is a long felt need for devices and methods to reduce the effects of sparking in an electrostatic precipitator.